I. Field of Invention
The invention generally relates to error detection in data compression, and more particularly to error detection in compressed digital image data.
II. Description of the Related Art
Video compression is a key factor of multimedia. An effective digital compression can reduce the cost as well as increase the quality of video displayed in any digital communication systems. One application of the video compression technique is in the motion picture industry.
For several decades, the motion picture industry has depended on the duplication, distribution, and projection of celluloid film for delivering programming material to geographically diverse theaters around the country and the world. To a large extent, the methods and mechanisms for the distribution of film material have remained relatively unchanged. Generally, the current film duplication and distribution process involves generating a master film copy from an exceptional quality camera negative, producing a distribution negative from the master film copy, and producing distribution prints from the distribution negative. Depending on the size of the release or number of copies desired for distributing the film, there may be more intermediate steps or multiple copies produced at each stage. The distribution prints (known as “positives”) are then distributed by physical means to various theaters and displayed using a film projector.
Although the distribution process above works, there are inherent limitations. Due to the use of celluloid material for the film and the bandwidth limitations of the film media, there are restrictions on the ability to provide high fidelity multi-channel audio programming. Then, there is the high expense of making a large number of film duplicates, which can cost several hundreds or thousands of dollars for each copy of a feature length film. There is also the expense, complexity, and delay associated with physically distributing large canisters of celluloid film to a large and growing number of theater locations. In addition, this type of film can easily be damaged during use and/or the quality can quickly degrade, thereby impacting the presentation experience.
Accordingly, new and emerging technologies are being developed to provide alternative approaches to the ongoing film distribution problems. One such method is the use of satellite transmission. However, in order to transmit a high quality audio/video (AV) signal in “real-time,” the data rate requirement (in bits per second) is on the order of 1.5 billion bits per second. This high data rate requires the capacity equivalent of an entire satellite to transmit even a single program, which is prohibitively expensive. Therefore, satellite transmissions are not yet commercially viable for the distribution of high quality AV material. Moreover, the received information must be displayed using a high quality projector, which has not previously been available. As a result, the implementation of a satellite based transmitter and receiver system would be costly and a radical change from current methods of film distribution and display.
Advances in digital technology have also led to a distribution concept whereby programming material is electronically stored in a digitized format. The digitized images may be distributed on various magnetic media or compact optical discs, or transmitted over wired, fiber optic, wireless, or satellite communication systems. These storage mediums typically have storage capacities ranging from about 4.5 gigabytes (GB) to about 18 GB. However, an average two hour movie having an average image compressed bit rate of about 40 Mbps for the image track and about eight Mbps for audio and control information requires approximately 45 GB of storage space. Thus, even if a high storage capacity DVD-ROM disk is implemented, a two-hour movie requires use of multiple DVD-ROM disks for adequate capacity.
To reduce the data rate requirement for the storage of high quality electronic images, compression algorithms are being developed. One digital dynamic image compression technique capable of offering significant compression while preserving the quality of image signals utilizes adaptively sized blocks and sub-blocks of encoded discrete cosine transform (DCT) coefficient data. This technique will hereinafter be referred to as the adaptive block size discrete cosine transform (ABSDCT) method. The adaptive block sizes are chosen to exploit redundancy that exists for information within a frame of image data. The technique is disclosed in U.S. Pat. No. 5,021,891, entitled “Adaptive Block Size Image Compression Method And System,” assigned to the assignee of the present invention and incorporated herein by reference. DCT techniques are also disclosed in U.S. Pat. No. 5,107,345, entitled “Adaptive Block Size Image Compression Method And System,” assigned to the assignee of the present invention and incorporated herein by reference. Further, the use of the ABSDCT technique in combination with a Discrete Quadtree Transform technique is discussed in U.S. Pat. No. 5,452,104, entitled “Adaptive Block Size Image Compression Method And System,” also assigned to the assignee of the present invention and incorporated by reference herein. The systems disclosed in these patents utilize intraframe encoding, wherein each frame of an image sequence is encoded without regard to the content of any other frame.
Technologies such as the ABSDCT compression technique offer the possibility of a “digital cinema” system. Generally defined, digital cinema refers to the electronic distribution and display of high quality film programming which has been converted to or prepared originally in a digital electronic representation for storage, transmission, and display purposes. A digital cinema system would overcome many of the limitations of the current film distribution process. A digital system would not be subject to the quality degradation over time experienced by celluloid film. Further, a digital system may eliminate the theft and illegal duplication of films by allowing implementation of security measures within the digital system itself. Moreover, distribution of film information using a digital electronic format actually increases the potential for rapid, low-cost duplication without quality degradation.
However, a complete digital cinema system has not been developed by the motion picture industry or related arts. In particular, even if film information can adequately be compressed for distribution, due to the large amount of data involved, an error may occur. For example, errors may occur during the compression, storage and/or decompression of the data. Also, errors may occur during transmission of the compressed data. Particularly, for real time delivery of information through wireless transmission, errors may be generated by high levels of interference that exist due to the nature of wireless channels. Because of these errors, portions of compressed data can be distorted, corrupted or even lost. Such errors in data often cause delays or make recovery of the original data difficult. Therefore, an error detection technique is needed to ensure reliability and efficiency of the compressed data information.